Biocatalysis using lipase encapsulated in microemulsion-based organogels in supercritical carbon dioxide

Lipases from Candida antarctica and Mucor miehei were encapsulated in lecithin water-in-oil (w/o) microemulsion-based organogels (MBG). These gels were formulated with either hydroxypropylmethyl cellulose (HPMC) or gelatin. The esterification of lauric acid and 1-propanol catalyzed by these MBGs was examined in supercritical carbon dioxide (scCO2; 35° C, 110 bar) as solvent for the substrates. The results were compared to those obtained with the reference substrate solvent isooctane. It turned out that the initial rates of this model reaction in scCO2 were higher than those observed in the reference system. Various parameters affecting the biocatalysis such as pressure, alcohol and acid chain length, and gel composition were investigated. Kinetic studies showed that the ester synthesis catalyzed by the immobilized C. antarctica lipase occurs via a Ping Pong Bi Bi mechanism in which only inhibition by excess of alcohol was identified. Values of all kinetic parameters were determined. In addition, experiments on the reusability of these gels in scCO2 were carried out and the state of water within the organogel was examined with the help of differential scanning calorimetry. The present study shows that biocatalysis using MBGs in scCO2 is a promising alternative to other bioconversion processes.